This invention relates to development systems for electrostatographic processors and, more particularly, to toner dispensers for development systems which utilize a multi-component developer.
In a conventional electrostatographic printing process, such as classical xerography, a more or less uniformly charged imaging surface is selectively discharged in an imagewise configuration to form a latent electrostatic image of the pattern to be printed. That pattern is then developed by applying an electroscopic marking material (commonly called "toner") to the imaging surface, and the developed image is thereafter fixed on the imaging surface (in a non-transfer mode of operation) or transferred to and fixed on a suitable copy substrate, such as plain paper (in a transfer mode of operation).
Typically, the toner is delivered to the imaging surface as a part of a dry multi-component developer comprising larger "carrier" particles in combination with finely-divided toner particles. The carrier and toner components are formed from materials which are displaced from one another in the triboelectric series so that they tend to acquire electrical charges of opposite polarity as they are blended and mixed together. Moreover, those materials are selected so that the charge imparted to the toner particles opposes the polarity of the latent image carried by the imaging surface.
To carry out the development process, the latent image-bearing imaging surface is customarily advanced through a development zone, while developer is being circulated along a path running from a sump, through the development zone and then back to the sump. Toner is electrostatically stripped from the developer which comes into actual contact with or into the immediate proximity of the imaging surface, thereby developing the image and reducing the toner concentration of the remaining or residual developer. For that reason, there ordinarily is a toner dispenser for adding fresh toner to the developer from time to time.
Substantial effort and expense have been devoted to the development of toner dispensers. One of the more efficient models proposed to date is disclosed and claimed in Hudson et al U.S. Pat. Re. No. 27,876, which issued Jan. 8, 1974, for "Dispensing Apparatus". Indeed, the toner dispenser of that patent is generally representative of the background of this invention and, therefore, the Hudson patent is hereby incorporated by reference.